My comments
The right tympanic bulla is distorted and difference in general appearance from the left tympanic bulla. There is cloudiness in the right tympanic bulla.

Case management
In this case, most likely vestibular signs as caused by right chronic otitis media/interna is the clinical diagnosis. The generalized muscle wasting and weight loss is most likely related to some type of nerve or muscle disease. I doubt that the otitis media/interna caused the generalized muscle wasting but could cause some weight loss. The potential muscle or nerve disease could be related to an immune-mediated disease; hence, a polymyositis or polyneuropathy. I really do not believe a brain tumor is involved. It could be possible that this dog could benefit from some short-term steroid administration.

Photo 2

Wrong interpretation
Because of the dog's worsening vestibular signs, the dog underwent MR imaging of the skull. T1-weighted and T2-weighted transverse images were first obtained. Intravenous contrast medium was administered and T1W transverse, sagittal and dorsal images were acquired. The findings of the MR imaging were as follows.

There is a 2-cm discretely bordered mass within the left half of the cerebellum with extension toward the brain stem and specifically includes the left seventh and eighth cranial nerves. This mass is mostly isotense to the normal brain tissue on T1-weighted images, but diffusely hyperintense on T2-weighted images.

The mass enhances with the contrast medium. The mass contains multiple, non-enhancing low T1-weighted and high T2-weighted signal foci consistent with cysts. The fourth ventricle is compressed and deviated to the right by the mass. The bullae and ear canals appear within normal limits.

MR diagnosis
Choroid plexus tumor arising from the cerebellopontine angle or fourth ventricle. Obstruction of the fourth ventricle is highly likely as this mass progresses and will lead to obstructive hydrocephalus.

Review of brain tumors
Brain tumors may be primary (arising from tissue inherent to the brain and its coverings) or secondary (reaching the brain by local extension or hematogenous metastasis).

The most common primary tumors of dogs are neuroepithelial (gliomas), meningeal (meningiomas) and lymphoid (reticulosis, lymphosarcoma) in origin. Glial cell neoplasms and pituitary gland tumors occur most commonly in brachycephalic breeds, while meningiomas are recognized most often in dolichocephalic breeds.

The brain is the most common site for metastasis of systemic neoplasms. Secondary tumors that are commonly associated with metastatic brain disease include nasal adenocarcinoma with its direct extension and distant metastasis from melanoma, hemangiosarcoma, mammary gland adenocarcinoma, pancreatic adenocarcinoma, undifferentiated carcinomas and adenocarcinoma of multiple origins.